The present invention is directed to the electrical connections of the slider of a head gimbal assembly. More specifically, the present invention pertains to clamping the test probes of a preamplifier board to the contact pads of the flexible printed circuit assembly of the head gimbal assembly.
FIG. 1 illustrates in an exploded view a prior art clamping system for connecting test probes to the test pads of the flexible printed circuit (FPC) of a head gimbal assembly (HGA). The HGA 102 with a FPC 104 is inserted into an indentation in a clamp 106. The FPC 104 has multiple test pads 108 accessible from both sides of the FPC, such as positive and negative read pads and positive and negative write pads. A cover 110 secures the FPC 104 in place on the clamp 106. In one embodiment, the cover is coupled to the clamp 106 by screws 112. The clamp is made of anti-static plastic having a surface resistivity between 1010 and 1012 ohms/square.
A preamplifier board 114 has one or more test probes 116 extending upward. A test probe housing 118 is coupled to the preamplifier board 114. In one embodiment, two plastic screws 120 are used to couple the test probe housing 118 to the preamplifier board 114. A grounding pad 122 can be placed around each of the screws to prevent discharge. The test probes 116 extend up through the test probe housing 118 and correspond to each of the bottom test pads on the FPC 104.
The test probe housing 118 is coupled to the clamp 106 by a rotary pin 124. FIG. 2a illustrates a diagram showing the clamp system in an open position, such as when the FPC is inserted into the clamp. FIG. 2b shows a close up cross-section of the clamping system in the open position. At this point, the test pads 108 of the FPC 104 are not in contact with the test probes 116.
A compression spring 126 forces the clamp 106 to rotate into contact with the test probe housing 118. FIG. 2c illustrates a diagram showing the clamp system in a closed position. FIG. 2d shows a close up cross-section of the clamping system in the closed position. At this point, the test pads 108 of the FPC 104 are forced into contact with the test probes 116.
The problem with this method is that the test probes 116 are brought into contact with the test pads 108 before the electrical potential difference, or voltage, between the two can be equalized. This can create a massive transient current discharge, which can lead to electro-static damage to the magnetic read/write head of the head gimbal assembly.